Tell pppd to set LNS mode flag on kernel pppol2tp session socket.

This flag is needed to set LNS mode on kernel socket for correct
functioning of pppd and xl2tpd in LNS mode.
+ use address from the last received UDP packet in UDP messages response
Merge pull request #25 from tchmelar/master

Use address from the last received UDP packet in UDP messages response
Merge pull request #22 from sigwall/kernel

Tell pppd to set LNS mode flag on kernel pppol2tp session socket.
Merge pull request #26 from PepeN/master

Minor fixes
Removed all of the trailing whitespace.